Question

(tga+ctga)^2-(tga-ctga)^2=4 докажите тождество 

Answer 1

 $(tga+ctga)^2-(tga-ctga)^2=A^2-B^2=\=(tga+ctga-(tga-ctga))(tga+ctga+tga-ctga)=\=2ctgacdot 2tga=4cdot (tgacdot ctga)=4cdot 1=4$